According to access methods, such as a Circuit Switched (CS), a Packet Switched (PS), and a Core Network (CN), a Global System for Mobile Communication (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE) system can be classified into three (3) classes, namely, Class A, Class B, and Class C. In Class A, a mobile station (MS) can receive the CS and the PS services simultaneously. In Class B, the MS can receive the CS service and the PS service but cannot receive both services simultaneously. In Class C, the MS can receive either the CS service or the PS service.
In the GSM/GPRS/EDGE system, a dedicated mode, a packet transfer mode, and a Dual Transfer Mode (DTM) can be supported. The dedicated mode indicates the MS having the CS connection, the packet transfer mode indicates the MS having the PS connection, and the DTM indicates the MS having both the CS and the PS connections.
According to conventional art, the GSM/GPRS system, which is represented by the CS connection, supports hard handover. In addition, the GSM/GPRS system also supports handover in connection with the PS connection.
The conventional art does not provide detail explanation of the handover procedure for the DTM. More specifically, if handover is takes place when the MS has the CS connection during DTM, then the PS connection is released, and the CS handover procedure is performed in a same manner as if the MS is in the dedicated mode. Alternatively, if only the CS connection is released in DTM, then the PS connection is also released, thus entering idle mode. Thereafter, the MS enters the packet transfer mode from idle mode.
Currently, a Wideband Code Division Multiple Access (WCDMA) system supports services that allow data from the CS connection and the PS connection to be received simultaneously. In addition, it is possible for handover procedure to take place between the WCDMA system and the GSM/GPRS/EDGE system. However, if the GSM/GPRS/EDGE system does not support handover procedure during DTM, then the services enjoyed in the WCDMA cannot be received. That is, the data through the CS connection and the PS connection cannot be simultaneously received during DTM of the GSM/GPRS/EDGE system.
Consequently, the MS cannot efficiently perform handover procedure. Furthermore, the MS cannot reflect or incorporate priority in performing handover procedure even if one of the CS or the PS is considered more important.